1. Field of the Invention
This invention relates to cameras, and more particularly to improvements of a camera having a program shutter.
2. Description of the Prior Art
Program shutters are known. However, in a camera having a conventional program shutter, when the Ev value determined by the film speed and the brightness of an object being photographed is invariable, that Ev value does not allow the selection of more than one combination of shutter speed and diaphragm aperture. Hence, it has been impossible to operate with an arbitrary value of shutter speed or diaphragm aperture. By providing an additional control circuit for diaphragm priority, or shutter priority exposure, it is of course possible to select an arbitrary value of shutter speed or diaphragm aperture. The drawback of using such a control circuit in the camera is that the circuitry of the camera increases in complexity, and its production cost is also raised. For this reason, proposals have been made to arbitrarily vary the program curve, for example, as in U.S. Pat. No. 4,103,307. However, in these program shutters, it is the gradient of the program curve that is varied. Therefore, the ratio of variation of the shutter time and diaphragm value to the variation of brightness cannot be maintained constant. This is a disadvantage.
Another program shutter which has solved the above drawback by determining the program formula itself on the basis of brightness, and determining a combination of diaphragm aperture and shutter time in accordance with the formula selected by the brightness is disclosed, for example, in DOLS 2645541. Since said program shutter responsive to the brightness selects the formula itself for determining the diaphragm and shutter time, the computation formula for determining the program becomes very complicated. It becomes necessary to perform the computation by using a microprogram and the like. Thus, there is a drawback that a microprocessor must be used as the computing circuit of the camera.